(Not Applicable)
This invention did not result in any way from finding or sponsorship of any governmental entity, including the Federal Government of the United States of America.
This invention relates to integrated circuit current mirror, and more specifically to such current mirrors requiring large but accurate multiplication ratios or low power supply voltage.
Current mirrors are used to establish the desired bias currents in transistors in integrated circuits. Typically an accurate bias current is developed in a single multiple transistor circuit. The design of these circuits to provide temperature compensated sources is not a subject of this patent, and can be found, for example, in textbooks such as Gray and Meyer (xe2x80x9cAnalysis and Design of Analog Integrated Circuitsxe2x80x9dxe2x80x94Paul Gray and Robert G. Meyer. Third Edition published by John Wiley and Sons 1997.) A reference current from such circuits is used, along with current mirrors, to establish the proper bias currents for many circuits. Current mirrors are used in both bipolar and MOS integrated circuits for biasing. The present invention improves the accuracy and reduces the operating voltage required for current mirrors.
This invention incorporates an elementary operational amplifier (opamp) as an integral part of various current mirrors. Use of an opamp provides accurate reproduction of the xe2x80x9crailxe2x80x9d (the node to which all the bases or gates in the mirror circuit are connected) voltage of the current mirror, and obviates the usual xe2x80x9chelperxe2x80x9d transistor, thus reducing the voltage required for the current mirror to function properly. While the opamp requires more transistors than the simple xe2x80x9chelperxe2x80x9d transistor, there are many applications where the lower operating voltage or better precision justify the additional silicon area required.